While the present invention can be effectively used in a plurality of paper-handling or marking systems, it will be described for clarity as used in finisher modules of electrostatic marking systems such as electrophotography. In an electrostatographic reproducing apparatus commonly used today, a photoconductive insulating member may be charged to a negative potential, thereafter exposed to a light image of an original document to be reproduced. The exposure discharges the photoconductive insulating surface in exposed or background areas and creates an electrostatic latent image on the member which corresponds to the image areas contained within the original document. Subsequently, the electrostatic latent image on the photoconductive insulating surface is made visible by developing the image with a developing powder referred to in the art as toner. During development, the toner particles are attracted from the carrier particles by the charge pattern of the image areas on the photoconductive insulating area to form a powder image on the photoconductive area. This image may be subsequently transferred or marked onto a support surface, such as copy paper to which it may be permanently affixed by heating or by the application of pressure. Following transfer of the toner image or marking, the copy paper may be removed from the system by a user or may be automatically forwarded to a finishing station where the copies may be collected, compiled, stapled and formed into books, pamphlets, or other sets. This invention will be described throughout in reference to paper collected after the finishing station processes are completed. It should be understood, however, that the present invention can be used in any systems where paper is collected in paper stacks.
As above noted, there are many marking systems that transport paper or other media after the paper is marked in marking step or steps. These marking systems could include electrostatic marking systems, non-electrostatic marking systems and printers or any other system where paper or other flexible media or receiving sheets are transported internally to an output device, such as a finisher and compiler station or stations and the subsequent stacking of paper after the compiler completes its functions.
These electrostatic marking systems have finisher and compilers located at a site after the receiving sheets (paper) have been marked with a toner. After finishing is completed, the paper is conveyed to a paper-stacking or collection device generally conveniently located at a bottom portion of the finisher module of a marking machine. A stacking cart generally used in one prior art is movable so that it can be moved into and out of the finisher paper collection module when loaded with paper. Current paper stacking involves the use of carts on casters for compiling paper stacks in printers. Once the carts are loaded, a manual process of unloading small stacks at a time from the main stack is needed. The finishing station is shut off while the stacked paper is being removed. Once the paper is removed, the finishing station is turned back on and the collection tray or stacker cart is replaced in the finishing collection station.
Traditional prior art stackers provide a single elevator platform which either stays in the stacker or is integrated into a cart for transport. Either way when the sheets are being removed from the system, the stacking operation is turned off. Unloading a stacker, a one-piece rigid platform or collection cart, either requires the stack to be removed from the tray or if a cart is used, the cart must be made to move into the stacker with the removal of a front lower frame support. The finisher is not running until the cart is replaced after unloading. Multiple stack trays cannot occupy the same vertical space because the tray must be raised and lowered along the same line.
Stacker designs usually provide for one stack and if multiple stacks are desired, multiple stacking locations are required. Often times this means additional stackers are required to be kept in reserve. Within stacker designs, two versions are commonly used. The first being a fixed elevator that moves up and down in a vertical space allowing for the stacking of media, the unloading of said media, and the reset of the elevator tray. As earlier noted, before the elevator can be reset, the stack must be unloaded. The time required to unload the elevator directly impacts the stacking function. Additionally, a problem known to stackers is the reset time required to move the elevator from the unload position back to the reset position. The second method commonly used in stacking is to provide the elevator function as part of a cart that can be used to unload the stacker. However, stacking cannot continue until the cart is replaced after the stack has been transported and removed. Because the cart is integral to stacking and the elevator tray is the cart, the front lower frame is removed from the stacker to allow for the cart to be moved into the stacker. This invention overcomes both of these problems without adding an additional stack or stacker module. By the use of an articulated shelf system, a rigid shelf can be formed for stacking while allowing for a flexible shelf system that can be transported out of the vertical space required by the elevator.